1. Field of the Invention
This invention relates to a process for separating boric acid compounds dissolved in water, particularly borate ions from an aqueous solution containing boric acid compounds at a low concentration such as sea water, with good selectivity and at high efficiency.
2. Description of the Prior Art
Borate ions exist natively in minute amounts in natural rivers, lakes or ponds, sea water and underground brine. When such water sources are utilized for agricultural purposes, the presence of boron at a level of 5 ppm or higher has been known to be detrimental to growth of agricultural crops.
Also, in the production of magnesium hydroxide from sea water, boric acid compounds dissolved in sea water at a level of 4 to 5 ppm as boron are co-precipitated with magnesium hydroxide, whereby the quality of refractory bricks produced by use of such magnesium hydroxide such as heat resistance will be lowered. Since these borate ions dissolved in minute amounts in water are overwhelmingly smaller in amount as compared to other co-existing anions, it is very difficult to selectively remove only borate ions.
Heretofore, as methods for separation of boric acid compounds dissolved in water, there have been proposed methods involving adsorption separation, using, for example, an anion exchange resin, or a chelate resin such as a boron-selective resin derived from a polyvalent alcohol or a metal hydroxide such as magnesium hydroxide or a hydrous zirconium oxide. However, the boric acid concentration is so low as 4 to 10 ppm as boron, and also due to the co-presence of a large amount of various ions, the above described methods are insufficient in boron selectivity or adsorbability. Thus, under the present situation, no economically effective method has been so far known.